Method of manufacturing aromatic urethanes

ABSTRACT

A method for manufacturing a purified aromatic urethane. Aromatic urethanes are synthesized from a N,N&#39;-disubstituted urea and an organic hydroxyl compound in a reaction medium. The organic hydroxyl compound and the primary aromatic amine side product which are present in the reaction mixture is distilled off and removed from the reaction mixture leaving a distillation bottom. The N,N&#39;-disubstituted urea is separated and removed from the distillation bottom by solvent extraction of the aromatic urethane, and the aromatic urethane in the extract phase obtained in said solvent extraction is separated and purified.

This is a division of application Ser. No. 07/495,353, filed Mar. 16,1990, now U.S. Pat. No. 5,130,464, issued Jul. 14, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing aromaticurethanes.

2. Description of the Related Art

U.S. Pat. No. 4,678,856 discloses a method wherein a primary aromaticamine, an aromatic nitro compound, and carbon monoxide are caused toreact together in the presence of a specified catalyst and solvent toproduce a N,N'-disubstituted urea, the urea obtained by this method inturn being caused to react with an organic compound containing hydroxylgroups to produce a primary aromatic amine and an aromatic urethane, thearomatic urethane then being separated and recovered from the reactionproduct. The above U.S. patent also discloses that aromatic amine isused as a solvent, the amount of which is over the quantity specified asbeing required for the reaction.

In U.S. patent application Ser. No. 07/825,822, an improvement of U.S.Pat. No. 4,678,856 is disclosed wherein nitriles, pyridines, quinolinesand cyclic ethers are used as solvents to stabilize the catalyst andprevent it from separating out. Use of such solvents prevent thecatalyst from separating out of the system together with crystals of theurea compound product, and permits the catalyst to be re-used.

SUMMARY OF THE INVENTION

The present invention specifically relates to an improvement of theinvention described in U.S. patent application Ser. No. 07/825,822, andproposes a different solvent to that disclosed therein.

The first objective of this invention is to provide a method ofmanufacturing aromatic urethanes in a two-step reaction, which comprisesmanufacture of ureas by carbonylation and the reaction of the ureasproduced using compounds containing hydroxyl groups, thereby improvingthe overall yield and selectivity, but which also permits ease ofrecovery of the catalyst and urethanes.

A second objective of this invention is to provide a method ofmanufacturing aromatic urethanes wherein at least a part of the solventused in the urea production reaction of the first step consists of asolvent which acts to stabilize the catalyst in solution to prevent itfrom separating out and also to improve the activity of the catalystthereof, thereby permitting efficient recycling of catalyst, increasingthe rate of the reaction of the first step, and increasing theefficiency of the method.

A third objective of this invention is to provide a method ofmanufacturing aromatic urethanes which does not involve the use ofhalogen compounds, whereby the problems inherent in their use are thusavoided.

In order to achieve the above objectives, this invention consists of amethod of manufacturing aromatic urethanes which comprises threeprocesses.

In the first process, an aromatic nitro compound, an aromatic primaryamine and carbon monoxide are caused to react together by use of acatalyst comprising a compound containing a platinum group metal,thereby producing N,N'-disubstituted urea. The solvent used hereconsists at least partly of a solvent (referred to hereafter as a firstsolvent) which stabilizes the catalyst to prevent it from separatingout, and increases its activity so as to maintain the catalyst stable insolution and increase the rate of the reaction. The N,N'-disubstitutedurea produced is then separated and isolated.

In the second process, the N,N'-disubstituted urea obtained in the firststep is caused to react with a compound containing hydroxyl groups toproduce a primary aromatic amine and an aromatic urethane, the latterbeing obtained by separation of the primary aromatic amine.

In the third process, the primary amine separated is recycled to thefirst process.

Additional objects and advantages of the invention will be set forth inthe description which follows, and will in part be obvious from thedescription, or may be learned through practice of the invention, whilethe objects and advantages of the invention may be realized and obtainedby means of the instrumentalities and combinations specifically pointedout in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

We shall now describe this invention in more detail.

In the first process, an aromatic primary amine, an aromatic nitrocompound and carbon monoxide are caused to react together by use of acatalyst consisting essentially of a platinum group metal, and by use ofthe first solvent having a coordination ability to catalyst metal as atleast part of the solvent. This reaction is considered to proceedaccording to the following equation: ##STR1##

The aromatic primary amine can be any one of anilines,aminonaphthalenes, aminoanthracenes and aminobiphenyls, specificexamples of such compounds being aniline, o-, m-and p-toluidine, o-, m-and p-chloroaniline, α and β naphthylamine, 2-methyl-1-aminonaphthalene,isomers of diaminobenzene, isomers of triaminobenzene, isomers ofaminotoluene, isomers of diaminotoluene, isomers of aminonaphthalene, ormixtures of these compounds.

The aromatic nitro compound can be any one of nitrobenzenes,nitronaphthalenes, nitroanthracenes, nitrobiphenyls, and anitro-compound wherein at least one of the hydrogen atoms is substitutedby for example a halogen atom, cyano group, alicyclic group, aromaticgroup, alkyl group, alkoxy group, sulfone group, sulfoxide group,carbonyl group, ester group, amide group, or the like, specific examplesof such compounds being nitrobenzene, o-, m-, and p-nitrotoluene,o-nitro-p-xylene, 2-methyl-1-nitronaphthalene, isomers ofdinitrobenzene, isomers of trinitrobenzene, isomers of dinitrotoluene,isomers of nitronaphthalene, o-, m-, and p-chloronitrobenzene,1-bromo-4-nitrobenzene, or mixtures of these compounds. The nitrocompound use should preferably correspond with the primary aromaticamine.

An amide compound added as first solvent can be any amide, specificexamples being N,N-dimethylacetamide, N,N-dimethylformamide, andN-methyl-2-pyrolidinone; a substituted urea represented by the generalformula: ##STR2## where R¹, R², R³, and R⁴ are alkyl groups and alkylenegroups with a carbon chain of 3-5 carbon atoms, specific examples ofsuch compounds being N,N,N',N'-tetramethylurea,1,3-dimethyl-2-imidazolidinone,1,3-dimethyltetrahydro-2(1H)-pyrimidinone; a phosphineamide compoundrepresented by the general formula: ##STR3## where R¹ and R² are alkylgroups with 1-5 carbon atoms, and n=1-5; a phosphine-amide compoundrepresented by the general formula: ##STR4## where R¹ and R² are alkylgroups with 1-6 carbon atoms, and alkylene groups with a chain of 3-5carbon atoms; or isomers or mixtures of these compounds.

An oxygen-containing organic sulfur compound used as first solventcomprises a sulfoxide represented by the general formula R¹ -SO-R² or R¹-SO₂ -R², wherein R¹ and R² are alkyl, alkoxy substituted, phenylsubstituted groups with 1-8 carbon atoms, and alkylene groups with achain of 4-7 carbon atoms, specific examples being dimethylsulfoxide,diphenylsulfoxide and sulfolane.

In this invention, the reaction of the first step may be carried outusing a solvent consisting substantially of the first solvent, or may becarried out in a mixture of the first solvent with other suitablesolvents. These other suitable solvents comprises an excess of aniline(referred to hereafter as a secondary solvent) compared to thetheoretical quantity required for the reaction; compounds which do notcontribute to the reaction, examples of which are aromatic hydrocarbonssuch as benzene, toluene, and xylene; halogenated aliphatic hydrocarbonssuch as mesitylene chlorohexane and chlorocyclohexane; and halogenatedaromatic hydrocarbons such as chlorobenzene, bromobenzene,dichlorobenzene and trichlorobenzene (referred to hereafter as atertiary solvent).

The carbon monoxide used may be pure, or it may contain nitrogen, argon,helium, carbon dioxide, or halogenated hydrocarbons.

The catalyst containing ruthenium or rhodium is a compound of rutheniumor rhodium with a ligand such as carbon monoxide or a phosphine, or withan organometallic compound containing organic groups, but it ispreferable that this compound does not contain halogen atoms. Specificexamples of such compounds are ruthenium complexes such as Ru₃ (CO)₁₂,H₄ Ru₄ (CO)₁₂, [Ru₂ (CO)₄ (HCOO)₂ ]_(n), Ru(CO)₃ (dppe), Ru(CO)₃ (PPh₃)₂and Ru(acac)₃ ; and rhodium complexes such as Rh₆ (CO)₁₆,RhH(CO)(PPh₃)₃, Rh(acac)(CO)(PPh₃), Rh(acac)(CO)₂ and Rh(acac)₃. PPh₃indicates triphenylphosphine, dppe indicates diphenylphosphinoethane,and acac indicates acetylacetonate.

In place of these complexes, inorganic platinum group metal compoundsmay be used which change into reactive species in the reaction system.Specific examples of such compounds are RuO₂.nH₂ O, Ru-black, and Rucarbon. These compounds change into carbonyl complexes to produce activespecies in the reaction system.

These platinum group metal compounds may also be used in combinationwith cobalt, iron, rhodium and palladium compounds or the like.

The reaction temperature is normally in the range 30°-300° C., andpreferably 120°-200° C. The reaction pressure is in the range 1-500kg/cm², and preferably 10-150 kg/cm². The reaction time varies accordingto reaction temperature, pressure, and other conditions, but normallytakes from several minutes to several hours.

The N,N'-substituted urea obtained by the method of this invention haslow solubility in solvents and in the aromatic amines and aromaticnitro-compounds which are used as starting materials. Therefore afterthe reaction is complete and the solution cooled to room temperature,the N,N'-substituted urea crystallizes and separates out, and may thusbe obtained in solid form in good yield by filtering the solution. Sincethe catalyst has been stabilized by the addition of the first solvent,and remains in the filtrate without separating out, it can thus bere-used as it is. Further, as the first solvent increases the activityof the catalyst, the reaction rate at which the reaction of the firststep takes palace is high. Since the first solvent has high solubilityin the N,N'-substituted urea produced by the reaction, a volume ofcrystallized N,N'-substituited urea may be controlled by adjusting anamount of the secondary and/or tertiary solvent.

After the reaction, when the solution is cooled to room temperature andthe product is crystallized out, constituents of the reaction mixtureapart from the disubstituted urea may easily be separated by rinsingwith solvents such as toluene and benzene, and the disubstituted ureamay therefore be obtained on its own.

Next, in the second process, the N,N'-disubstituted urea obtained ismade to react with an organic compound containing hydroxyl groupsaccording to the following equation, to produce a primary aromatic amineand an aromatic urethane: ##STR5##

In this reaction, the N,N'-disubstituted urea used as starting materialis one substituted on nitrogen atom by organic groups chosen from amongaliphatic groups, alicyclic groups, or aromatic groups. The substitutinggroups may be either identical or different, but at least one of themshould be aromatic. The N,N'-disubstituted ureas may be N,N'-diarylureas, with ureas having amino substituents on the aromatic ring--suchas, for example N,N'-diphenylurea--being particularly suitable.

The organic compound containing hydroxyl groups of this invention may,for example, be a monohydric alcohol, a polyhydric alcohol, or amonohydric or polyhydric phenol, and of these, a monohydric alcohol, aphenol, or a mixture of the two is to be preferred. Specific examples ofmonohydric alcohols are methyl alcohol, ethyl alcohol, n-propyl alcohol,isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and t-butylalcohol. Specific examples of monohydric phenols, apart from phenolitself, are chlorophenol, phenols with alkyl groups such as methyl,ethyl, n-propyl, and isopropyl, and their isomers. Alcohols are to bepreferred to phenols, and methanol and ethanol are to be particularlypreferred.

The reaction which produces an aromatic urethane from aN,N'-disubstituted urea and an organic compound containing hydroxylgroups is reversible, and in this invention, the equilibrium between theforward and back reactions is controlled by the amount of organichydroxyl compounds in the reaction system. The reaction equivalents are1 mole of hydroxyl compound per 1 mole of N,N'-disubstituted urea, butto promote the forward reaction, a large excess of hydroxyl compoundmust be used. Thus, in this invention, 1-100 moles of hydroxyl compoundis used per 1 mole of N,N'-disubstituted urea. As an indication, theamount of hydroxyl compound used must be such that the molar ratio ofaromatic urethane (X) to N,N'-disubstitued urea (Y) in the productionsystem, (X/Y), is no less than 20 and preferably in the range of 20-50.

The above urethane synthesis reaction proceeds under the followingconditions. The reaction temperature is in the range 80°-300° C., andpreferably 120°-200° C. The reaction pressure is the autogenous pressureat the reaction temperature employed--for example, in the range 1-200atm, and preferably 1-50 atm. The reaction time varies according toreaction temperature, pressure and other conditions, and also accordingto the type of N,N'-disubstituted urea and organic hydroxyl compound,but normally takes from several minutes to several hours.

In this invention, the desired aromatic urethane is separated fromunreacted N,N'-disubstituted urea, concurrently formed primary amine,and organic hydroxy compound as follows. Of the above three compounds,the organic hydroxyl compound and the aromatic primary amine are removedby continuous or batch distillation. Whichever of these distillationmethods is used, the number of theoretical plates, the reflux ratio, andthe level of internal column pressure may be chosen arbitrarily,provided that the aromatic urethane--remaining at the bottom duringcontinuous distillation or as a still residue in the case of batchdistillation--does not decompose and the N,N'-disubstituted urea doesnot separate out. However, as aromatic urethanes decompose rathereasily, it is therefore preferable that the internal column pressure beno greater than 760 mmHg. Further, while the use to which the organichydroxyl compound and primary aromatic amine ar put after they have beenremoved by distillation is a matter of choice, it is, howeveradvantageous if they are re-used as reaction starting materials employedin the first step; in particular, it is preferable that the organichydroxy compound be recycled into the reaction system and reused in thismanner.

After the above three compounds have been removed by distillation, theonly substantial compound remaining in the reaction system is theN,N'-disubstituted urea, any other compounds present in the reactionsystem will be only a trace amount of reaction by-products. In thepresent invention, the desired aromatic urethane is separated from allremaining compounds by solvent extraction, this being accomplished byadding a suitable solvent to the production system, to selectivelyextract the urethane. The solvent used for this may be chosen from amonga number of types, all of which are capable of selectively extractingthe urethane; several of these solvents may be mixed together. However,of the various solvents suitable for this purpose, organic solvents suchas n-hexane, cylcohexane, benzene toluene, and dichlorobenzene areparticularly preferable.

The above solvent extraction process is carried out at a temperature inthe range 0°-150° C., and preferably 15°-100° C. The extraction pressureis the autogenous pressure of the system. As before, the extraction timevaries according to the reaction temperature and pressure, and alsoaccording to the type of the N,N'-disubstituted urea and the aromaticurethane, but normally takes from several minutes to several hours. Thisextraction process also may be a continuous or a batch operation. Theextract phase obtained from the above solvent extraction process is amixture of the solvent used and the extracted aromatic urethane. Theextract residue, on the other hand, is the N,N'-disubstituted urea, orin some cases a mixture of the N,N'-disubstituted urea and minuteamounts of side products, and may be either a liquid or solid.

Next, the aromatic urethane is recovered from the extract phase andpurified. This may be done by means of distillation, recrystallizationand/or crystallization. The choice of method used and the operatingconditions are based on the physical properties of the solvent and ofthe aromatic urethane (vapor-liquid equilibrium, solid-liquidequilibrium and thermal stability, etc). If, for example, the thermalstability of the aromatic urethane is low, cooling crystallization isused. Further, this process is used for solvent-aromatic urethanesystems even in which the solubility of the aromatic urethane variesmarkedly. Distillation, recrystallization, or crystallization may beeither continuous or batch operations.

In this invention, as stated earlier, the method of using the extractresidue is a matter of choice. However, since the residue consists ofN,N'-disubstituted urea, which is a starting material of the secondreaction step, and since any other substances present therein, will beonly a trace amount of reaction byproducts, it is therefore preferablethat this residue be recycled back into the reaction system of thesecond reaction step, and re-used in this manner.

Similarly, the use made of the liquid remaining after the aromaticurethane has been recovered and purified from the extract phase is amatter of choice; however, it is preferable that it too be recycled, andre-used as extraction solvent.

When the first process (reaction equation (1)) and the second process(reaction equation (2)) are carried out in sequence, the primaryaromatic amine does not undergo any actual change, and only the aromaticnitro-compound enters into the reaction. Overall, the aromaticnitro-compound is reductively transformed into the aromatic urethane,and this is more economical than using the primary aromatic amine as astarting material.

To summarize the advantages of this invention, therefore, since theN,N'-disubstituted urea produced in the first reaction step has lowsolubility in the solvent and the primary aromatic amine or aromaticnitro-compound, it can be easily crystallized by cooling to roomtemperature, and recovered in good yield by filtering. Further, sincethe activity of the catalyst is also improved by the first solvent, thereaction efficiency of the first step is increased. Moreover, since thecatalyst stabilized by the first solvent is in the form of a solution,it can be re-used in the first reaction step economically.

In addition, as there is no need to use halogen compounds in thisinvention, little corrosion of the equipment material occurs, and thusthere is no need for the reaction vessel be made from high-costmaterial.

Also, as few side reactions occur in the first reaction step, theN,N'-disubstituted urea may be obtained in high yield.

Further, as there is no need to use a catalyst in the second reactionstep, the aromatic urethane may be recovered as a distillation residueinstead of it having to be distilled off. Moreover, as the primaryaromatic amine which is distilled and the organic compound with hydroxylgroups have relatively low boiling points, the distillation may beconducted under mild conditions, thus making the operation easy toperform. Additionally, the primary aromatic amine which is recovered maybe re-used for the production of the N,N'-disubstituted urea of thefirst reaction step. Finally, the second reaction step takes placewithout a catalyst, proceeds almost constantly and produces few sideproducts. Consequently although the reaction is two-step, the aromaticurethane may be manufactured in high yield.

EXAMPLES

We shall now describe specific examples of this invention. Instead ofusing the common generic name "urethane" in these examples, we shall usethe term "N-alkyl carbamate" and clearly define the names of eachsubstance.

EXAMPLE 1

Into a 200 ml autoclave equipped with a magnetic stirrer were introduced5.6 g of nitrobenzene, 7.8 g of aniline, 27 ml of toluene, 6.3 g ofN,N,N',N'-tetramethylurea (referred to hereafter as TMU), and 20 mg ofRu₃ (CO)₁₂. Thereafter the atmosphere within the system was changed toone of carbon monoxide, within was set at a pressure of 50 kg/cm².Subsequently the reaction was carried out at 160° C. for 2 hours, withcontinuous stirring. After completion of the reaction, the system wascooled to room temperature, and following gas evacuation, the reactionliquor was filtered and 3.5 g of N,N'-diphenyl urea crystals obtained.The filtrate was analyzed by gas chromatography and high speed liquidchromatography, and found to contain 0.1 g of N,N'-diphenyl urea and 2.9g of nitrobenzene. This indicated that the TOF (Turn Over Frequency) ofN,N'-diphenyl urea production was 100 h⁻¹ based on catalyst metal atoms,and the selectivity based on nitrobenzene was 94%.

Next, 3.0 g of the isolated N,N'-diphenyl urea crystals were placedalong with 50 g of methanol in another 200 ml autoclave equipped with amagnetic stirrer, and a reaction was carried out at 160° C. for 3 hours.After this reaction was complete, the reaction liquor was analyzed bygas chromatography, which indicated that the yield of methylN-phenylcarbamate was 96%, and the yield of aniline was 95%.

EXAMPLE 2

The experimental production of N,N'-diphenyl urea was carried out usingthe same equipment and method as in Example 1, except that the quantityof TMU was 16.4 g and the quantity of toluene was 15 ml. The results ofthis experiment are shown in Table 1.

Further, 3.0 g of the isolated diphenyl urea and 50 g of methanol weremade to react together, using the same equipment and method as inExample 1. The yields of methyl N-phenyl carbamate and aniline wererespectively 95% and 94%.

COMPARATIVE EXAMPLE 1

The experimental production of N,N'-diphenyl urea was carried out usingthe same equipment and method as in Example 1, except that no TMU wasadded, and the quantity of toluene was 32 ml. The results of thisexperiment also are shown in Table 1.

COMPARATIVE EXAMPLE 2

The experimental production of N,N'-diphenyl urea was carried out usingthe same equipment and method as in Example 1 except that pyridine wasadded instead of TMU. The results of this experiment also are shown inTable 1.

COMPARATIVE EXAMPLE 3

The experimental production of N,N'-diphenyl urea was carried out usingthe same equipment and method as in Example 1 except that benzonitrilewas added instead of TMU. The results of this experiment also are shownin Table 1.

EXAMPLES 3-8

The experimental production of N,N'-diphenyl urea was carried out usingthe same equipment and method as in Example 1, except that the firstsolvent used in the previous examples was changed to DMI or NMP inExample 4-8. The results of this experiment are shown in Table 2.

Further, 3.0 g of the isolated diphenyl urea and 50 g of methanol weremade to react together, using the same equipment and method as inExample 1, to experimentally produce methyl N-phenyl carbamate andaniline. The results of this experiment are shown in Table 3.

EXAMPLE 9

The experimental production of N,N'-diphenyl urea was carried out usingthe same equipment and method as in Example 1 except that the catalystwas changed to [Ru₂ (CO)₄ (HCOO)₂ ]_(n). The results of this experimentare shown in Table 4.

Further, 3.0 g of the isolated diphenyl urea and 50 g of methanol weremade to react together, using the same equipment and method as inExample 1. The yields of methyl N-phenyl carbamate and aniline were each95%.

EXAMPLE 10 Synthesis Reaction for Aromatic Urethanes

The reaction was carried out using the following starting materials andunder the following conditions:

    ______________________________________                                        Starting Materials                                                            N,N'-diphenyl urea:                                                                              20 g                                                       Ethanol:           50 ml                                                      Conditions                                                                    Reaction temperature:                                                                            170° C.                                             Reaction time:     180 min                                                    Pressure:          Autogenous                                                 Reaction vessel:   200 ml autoclave with                                                         magnetic stirrer                                           ______________________________________                                    

In this reaction, the conversion of N,N'-diphenyl urea (referred tohereafter as DPU) was 97.5%, and that yield of the ethyl ester ofN-phenyl carbamate (referred to hereafter as EPC), which was the desiredproduct, was also 97.5%. The selectivity of EPC in this reactiontherefore was 100%.

Removal of Impurities by Distillation, 1

1 l of reaction product obtained as above was distilled under thefollowing conditions:

    ______________________________________                                        Starting material composition (mole %):                                       ______________________________________                                        Ethanol                79.1 mole %                                            Aniline                10.3 mole %                                            EPC                    10.3 mole %                                            DPU                     0.3 mole %                                            Amount introduced:     1 l                                                    Type of distillation:  Batch                                                  Number of theoretical plates:                                                                        10                                                     Reflux ratio:          5                                                      Pressure at top of column:                                                                           50 mmHg                                                ______________________________________                                    

After distillation of 80 mole %, the compositions of the distillate andof the still residue were examined, and the following results wereobtained:

    ______________________________________                                        Constituent                                                                              Distillate Still Residue (mole %)                                  ______________________________________                                        Ethanol    98.9 mole %                                                                                0 mole %                                              Aniline     1.1 mole %                                                                              47.0 mole %                                             EPC          0 mole % 51.5 mole %                                             DPU          0 mole %  1.5 mole %                                             ______________________________________                                    

Removal of Impurities by Distillation, 2

The still residue obtained as above was distilled under the followingconditions:

    ______________________________________                                        Amount introduced:      200 ml                                                Type of distillation:   Batch                                                 Number of theoretical plates:                                                                         10                                                    Reflux ratio:           5                                                     Pressure at top of column:                                                                            5 mmHg                                                ______________________________________                                    

After distillation of 48 mole %, the compositions of the distillate andof the still residue were examined, and the following results wereobtained:

    ______________________________________                                        Constituent   Distillate Still Residue                                        ______________________________________                                        Aniline       97.9 mole %                                                                                0 mole %                                           EPC            2.1 mole %                                                                              97.1 mole %                                          DPU             0 mole %  2.9 mole %                                          ______________________________________                                    

Removal of DPU by Solvent Extraction

To 50 g of the still residue obtained in the "Removal of Impurities byDistillation, 2" above, was added 120 g of n-hexane. After heating to60° C., a solid-liquid separation was performed in a centrifugal filter,with this temperature being maintained. The amounts of filtrate andsolid phase recovered, and the compositions thereof, were as follows:

    ______________________________________                                                      Filtrate       Solid Phase                                      ______________________________________                                        Amount recovered (g)                                                                          168.6  g         1.4  g                                       Composition:                                                                  n-hexane        71.1   mole %    5.0  mole %                                  EPC             28.8   mole %    2.1  mole %                                  DPU             0.1    mole %    92.9 mole %                                  ______________________________________                                    

Purification of EPC

100 g of the filtrate obtained above were cooled from 60° C. to 25° C.,and a solid-liquid separation was performed in a centrifugal filter,with the temperature of 25° C. being maintained. The amounts of filtrateand solid phase recovered, and the compositions thereof, were asfollows:

    ______________________________________                                                      Filtrate       Solid Phase                                      ______________________________________                                        Amount recovered (g)                                                                          74.3   g         25.7 g                                       Composition:                                                                  n-hexane        96.7   mole %    0    mole %                                  EPC             3.3    mole %    99.6 mole %                                  DPU             0      mole %    0.4  mole %                                  ______________________________________                                    

EXAMPLE 11

The filtrate obtained in the "Removal of DPU by Solvent Extraction" ofExample 10 was distilled under the following conditions:

    ______________________________________                                        Amount introduced:      50 ml                                                 Type of distillation:   Batch                                                 Number of theoretical plates:                                                                         10                                                    Reflux ratio:           5                                                     Pressure at top of column:                                                                            5 mmHg                                                ______________________________________                                    

After distillation of 72 mole %, the compositions of the distillate andof the still residue were examined, and the following results wereobtained:

    ______________________________________                                        Constituent   Distillate Still Residue                                        ______________________________________                                        n-hexane      98.9 mole %                                                                                0 mole %                                           EPC            1.2 mole %                                                                              99.6 mole %                                          DPU             0 mole %  0.4 mole %                                          ______________________________________                                    

EXAMPLE 12 Synthesis Reaction for Aromatic Urethanes

The reaction was carried out with the following starting materials andunder the following conditions:

    ______________________________________                                        Starting Materials                                                            N,N'-diphenyl urea:                                                                              5 g                                                        Methanol:          50 ml                                                      Conditions                                                                    Reaction temperature:                                                                            140° C.                                             Reaction time:     120 min                                                    Pressure:          Autogenous                                                 Reaction vessel:   200 ml autoclave with                                                         magnetic stirrer                                           ______________________________________                                    

In this reaction, the conversion of N,N'-diphenyl urea (referred tohereafter as DPU) was 95.3%, and the yield of the methyl ester ofN-phenyl carbamate (referred to hereafter as MPC), which was the desiredproduct, was 95.0%. The selectivity of MPC in the reaction was therefore99.7%

Removal of Impurities by Distillation, 1

1 l of reaction product obtained as above was distilled under thefollowing conditions:

    ______________________________________                                        Starting material composition (mole %):                                       ______________________________________                                        Methanol               93.5 mole %                                            Aniline                3.2 mole %                                             EPC                    3.2 mole %                                             DPU                    0.1 mole %                                             Amount introduced:     1 l                                                    Type of distillation:  Batch                                                  Number of theoretical plates:                                                                        10                                                     Reflux ratio:          5                                                      Pressure at top of column:                                                                           50 mmHg                                                ______________________________________                                    

After distillation of 94 mole %, the compositions of the distillate andof the still residue were examined, and the following results wereobtained:

    ______________________________________                                        Constituent                                                                              Distillate Still Residue (mole %)                                  ______________________________________                                        Methanol   99.5 mole %                                                                                0 mole %                                              Aniline     0.5 mole %                                                                              45.0 mole %                                             MPC          0 mole % 53.3 mole %                                             DPU          0 mole %  1.7 mole %                                             ______________________________________                                    

Removal of Impurities by Distillation, 2

The still residue obtained above was distilled under the followingconditions:

    ______________________________________                                        Amount introduced:      50 ml                                                 Type of distillation:   Batch                                                 Number of theoretical plates:                                                                         10                                                    Reflux ratio:           5                                                     Pressure at top of column:                                                                            5 mmHg                                                ______________________________________                                    

After distillation of 46 mole %, the compositions of the distillate andof the still residue were examined, and the following results wereobtained:

    ______________________________________                                        Constituent   Distillate Still Residue                                        ______________________________________                                        Aniline       97.8 mole %                                                                                0 mole %                                           EPC            2.2 mole %                                                                              96.9 mole %                                          DPU             0 mole %  3.1 mole %                                          ______________________________________                                    

Removal of DPU by Solvent Extraction

To 25 g of the still residue obtained in the "Removal of Impurities byDistillation, 2" above was added 60 g of n-hexane. After heating to 60°C., a solid-liquid separation was performed in a centrifugal filter,with this temperature being maintained. The amounts of filtrate andsolid phase recovered, and the compositions thereof, were as follows:

    ______________________________________                                                      Filtrate       Solid Phase                                      ______________________________________                                        Amount recovered (g)                                                                          84.1   g         0.9  g                                       Composition:                                                                  n-hexane        71.2   mole %    0.6  mole %                                  EPC             28.7   mole %    0.2  mole %                                  DPU             0.1    mole %    99.2 mole %                                  ______________________________________                                    

Purification of MPC

50 g of the filtrate obtained above were cooled from 60° C. to 15° C.,and a solid-liquid separation was performed in a centrifugal filter,with the temperature of 15° C. being maintained. The amounts of filtrateand solid phase recovered, and the compositions thereof were as follows:

    ______________________________________                                                      Filtrate       Solid Phase                                      ______________________________________                                        Amount recovered (g)                                                                          37.2   g         12.8 g                                       Composition:                                                                  n-hexane        95.7   mole %    0    mole %                                  MPC             4.3    mole %    99.4 mole %                                  DPU             0      mole %    0.6  mole %                                  ______________________________________                                    

As can be seen from Examples 10-12, no catalyst is used in the abovetwo-step process. Consequently, this disperses with the need forcomplex--and costly--operations for separating and recovering thecatalyst from the reaction system, and further, there is no corrosion ofmetal parts, as would occur were chlorinated catalysts or the like to beused. In addition, the selectivity of the desired aromatic urethanesfrom N,N'-disubstituted ureas in this invention is high, and there arepractically no side products. Therefore aromatic urethanes can beproduced in a more cost-efficient manner, since only the organichydroxyl compounds, aromatic amines, and N,N'-disubstituted ureas haveto be removed from the reaction system.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and illustrated examples shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

                                      TABLE 1                                     __________________________________________________________________________    Quantity introduced                                                                                    First     Selec-                                           Ru.sub.3 (CO).sub.12                                                                PhNO.sub.2                                                                        PhNH.sub.2                                                                        Toluene                                                                            solvent                                                                             TOF tivity                                     Example                                                                             (mg)  (g) (g) (ml) (g)   (h.sup.-1)                                                                        (%)                                        __________________________________________________________________________    1     20    5.6 7.8 27   TMU* 6.3                                                                            100 94                                         2     20    5.6 7.8 15   TMU 16.4                                                                            137 94                                         Compara-                                                                            20    5.6 7.8 32   0     56  98                                         tive                                                                          Example                                                                       2     19    5.4 9.6 21   Py* 9.2                                                                             46  90                                         3     20    5.5 9.5 19   PhCN* 9.6                                                                           40  94                                         __________________________________________________________________________     TMU: N,N,N',Ntetramethylurea                                                  Py: Pyridine                                                                  PhCN: Benzonitrile                                                       

                                      TABLE 2                                     __________________________________________________________________________    Quantity introduced                                                                                    First     Selec-                                           Ru.sub.3 (CO).sub.12                                                                PhNO.sub.2                                                                        PhNH.sub.2                                                                        Toluene                                                                            solvent                                                                             TOF tivity                                     Example                                                                             (mg)  (g) (g) (ml) (g)   (h.sup.-1)                                                                        (%)                                        __________________________________________________________________________    3     20    5.6 7.6 30   TMU 2.8                                                                              76 93                                         4     20    5.6 7.8 23   TMU 9.0                                                                             111 93                                         5     20    5.6 8.2 32   DMI* 3.0                                                                             90 94                                         6     20    5.6 8.2 23   DMI 8.9                                                                             109 94                                         7     20    5.6 7.9 30   NMP* 3.1                                                                             92 95                                         8     20    5.6 9.5 23   NMP 9.3                                                                             143 94                                         __________________________________________________________________________     DMI: 1,3dimethyl-2-imidazolidinone                                            NMP: NmethyI-2-pyrolidinone                                              

                  TABLE 3                                                         ______________________________________                                                      MPC yield Aniline yield                                         Example       (%)       (%)                                                   ______________________________________                                        3             95        94                                                    4             94        94                                                    5             95        95                                                    6             93        93                                                    7             96        94                                                    8             96        94                                                    ______________________________________                                         MPC: Methyl Nphenyl carbamate                                            

                                      TABLE 4                                     __________________________________________________________________________    Quantity introduced                                                                                    First     Selec-                                          Catalyst                                                                           PhNO.sub.2                                                                         PhNH.sub.2                                                                         Toluene                                                                            solvent                                                                            TOF  tivity                                     Example                                                                            (mg) (g)  (g)  (ml) (g)  (h.sup.-1)                                                                         (%)                                        __________________________________________________________________________    3    A 20 5.6  7.6  30   TMU 2.8                                                                            76   93                                         9    B 20 5.6  7.7  27   TMU 2.6                                                                            86   98                                         __________________________________________________________________________     A: Ru.sub.3 (CO).sub.12                                                       B: [Ru.sub.2 (CO).sub.4 (HCOO)2]n                                        

What is claimed is:
 1. A method for manufacturing an aromatic urethane,wherein said urethane is synthesized without the use of a catalyst, andthe urethane produced is purified, said method comprising:(a) reacting aN,N'-disubstituted urea and an organic hydroxyl compound to form areaction mixture containing an aromatic urethane and as a by-product, aprimary aromatic amine, (b) distilling the reaction mixture from step(a) to distill off and remove said organic hydroxyl compound and theprimary aromatic amine, wherein a distillation bottom product is formed,said distilling being performed under a reduced pressure, whereby theboiling point of the aromatic urethane decreases to its decomposingtemperature thereof or less, so as to prevent the decomposition of thearomatic urethane in the reaction mixture, (c) separating and removingthe N,N'-disubstituted urea from the distillation bottom productobtained in step (b), by solvent extraction to form an extract phase,and (d) separating and purifying the aromatic urethane in the extractphase.
 2. The method according to claim 1, wherein said step (a) iscarried out at a temperature of 100°-300° C. and a pressure of 1-200atm.
 3. The method according to claim 1, wherein said step (d) forseparating and purifying the aromatic urethane comprises distillation,recrystallization and crystallization processes.
 4. The method accordingto claim 1, wherein in said step (a) the N,N'-disubstituted urea is aN,N'-diaryl urea.
 5. The method according to claim 1, wherein in saidstep (a) said organic hydroxyl compound is selected from the groupconsisting of monohydric alcohols, polyhydric alcohols, monohydricphenols, polyhydric phenols, and mixtures thereof.
 6. The methodaccording to claim 4, wherein the N,N'-diaryl urea is N,N'-diphenylurea.7. The method according to claim 5, wherein said organic hydroxylcompound is selected from the group consisting of methyl alcohol, ethylalcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutylalcohol, t-butyl alcohol, phenol, chlorophenol and phenol substitutedwith a alkyl group selected from the group consisting of methyl, ethyl,n-propyl and isopropyl.
 8. The method according to claim 7, wherein1-100 moles of said hydroxyl compound are used per 1 mole of saidN,N'-disubstituted urea.
 9. The method according to claim 8, whereinstep (a) is carried out at a temperature of 120° to 200° C. and at apressure of 1 to 50 atmospheres.
 10. The method according to claim 9,wherein step (c) is carried out at a temperature of 0° to 150° C. 11.The method according to claim 9, wherein step (c) is carried out at atemperature of 15° to 100° C.
 12. The method according to claim 11,wherein the N,N'-disubstituted urea is N,N'-diphenylurea and the organichydroxyl compound is ethanol or methanol.
 13. The method according toclaim 1, wherein the distilling in step (b) is carried out at a pressureof no greater than 50 mmHg.
 14. The method according to claim 13,wherein the pressure is 5 mmHg.
 15. The method according to claim 13,wherein the pressure is 5 to 50 mmHg.
 16. The method according to claim1, wherein the N, N'-disubstituted urea is N, N'-diphenyl urea; theorganic hydroxyl compound is ethanol; the reaction mixture includesethanol, aniline, ethyl carbanilate and N, N'-diphenyl urea and thedistilling is carried out at a pressure of 50 mmHg or less.